(1) Field of Invention
The present invention relates to a method for determining an artificial impedance surface and, in particular, to a method for determining an optimized artificial impedance surface by calculating actual surface wave profiles supported on the impedance surface.
(2) Description of Related Art
The closest related art for the creation of artificial impedance surfaces is disclosed in U.S. Pat. No. 7,218,281 to Sievenpiper et al., herein incorporated by reference (hereinafter “Sievenpiper et al.”). Sievenpiper et al. discloses how to create an artificial impedance surface using metal patterning in order to scatter a given excitation into a desired far field radiation pattern. This method of creating the surface patterning relies on a radiofrequency holographic technique, where the impedance pattern is determined from the interference of a surface wave and the desired outgoing wave. Sievenpiper et al. uses only assumed surface wave profiles when determining the impedance pattern. However, due to the effects of edge scattering from the edges of the surface, the details of the feed excitation, and the local variation in surface wave wavenumber due to the local variation in the artificial impedance value, the actual surface wave profiles produced on the impedance surface are different than the assumed surface wave profile. Using only an assumed surface wave profile therefore results in less than optimal efficiency of conversion from excitation input power to the desired far field radiation pattern.
Thus, a continuing need exists for a method of creating an optimized impedance pattern based on the actual currents supported on the impedance surface.